眼か下壁骨折（Ｂｌｏｗ‐ｏｕｔ ｆｒａｃｔｕｒｅ）のＣＴ診断 ＣＴ２方向撮影による評価

Abstract

Diagnosis of a blow-out fracture of the orbital floor is relatively easy from clinical and roentogen findings but information from these findings are not adequate for the decision for surgical indication.Until recently, computed tomography for the orbital region was generally performed only in axial plane. But the axial plane is parallel to the orbital structure, therefore it is difficult to visualize the orbital floor and inferior rectus muscle. On the other hand, coronal plane is cross-section to the orbital structure, and we can visualize the all orbital soft tissues including extraocular muscles.We examined 3 cases diagnosed as a blow-out fracture of the orbital floor by conventional roentogen films and clinical findings. After axial CT was performed firstly, the coronal CT was scanned with 60 degrees to 70 degrees from OM line, setting the patient in the hanging head position.Case 1 used coronal reformation of the axial CT data. Case 2 and case 3 used direct coronal scanning. By bi-plane CT we could diagnose whether inferior rectus muscle was entrapped or not, and confirm surgical indication.Using of a cadaver, we studied the mechanism for limitation of eye movement. These studies revealed that it is rare that the inferior rectus muscle is entrapped directly by fractured segments at the orbital anterior floor. Because there is a lot of orbital fat-pad between the inferior rectus muscle and the orbital floor, and it may play an important role.The limited mobility of the inferior rectus muscle may occur as a result of increased tension of the fibrous bands that attach to the muscle sheath from the prolapsed fat-pad, and contructure by scar formed secondarily.Diagnosis of the location of a fracture in the orbital floor and cause of the limitation of eye movement must be done as early as possible and from this information we can confirm surgical indiction. We believe the bi-plane CT is one of the most useful methods for making a management plan of blow-out fractures of the orbital floor.